The following article was written with some of my points and questions with material provided as well by Gemini and edited by ChatGPT...
Scientists at the City University of New York have demonstrated what is often described as the “time reversal” of an electromagnetic wave using a specially engineered metamaterial. If an electromagnetic wave were a loaf of bread baked from dough, this process would not literally turn the loaf back into dough—but it would force heat to mathematically flow backward, retracing its original path with uncanny precision.
This distinction matters.
What is reversed is not time itself, but the evolution of the wave. The material imposes conditions that cause the electromagnetic wave to reverse its phase and momentum, sending it back along the exact trajectory from which it came. Some call this time reversal; others argue it is more accurately described as phase conjugation or wavefront reversal. The debate is not semantic—it cuts to the meaning of time in physics.
Time is often treated as a physical change in configuration and relation among objects within spacetime. Electromagnetic waves, however, are composed of massless photons. This raises an obvious question: if photons have no mass and do not experience proper time, in what sense can they be said to move “through time” at all—let alone have that motion reversed?
The electromagnetic field does not arise from the Higgs field. The Higgs field gives mass to certain particles—electrons, quarks, and the W and Z bosons—but photons do not interact with it and therefore remain massless. Electromagnetic waves are generated by accelerating electric charges, not by the Higgs mechanism. The EM field and the Higgs field are distinct and fundamental.
So how can a massless wave be time-reversed?
The answer is that mass is irrelevant here. Time reversal in these experiments refers to the symmetry of the wave equations themselves. Maxwell’s equations are largely time-symmetric. Under the right conditions, one can engineer a material system that causes a wave to propagate backward, undoing dispersion and scattering as if the clock were running in reverse. But the cosmic arrow of time is untouched.
If a massless particle’s wave vector reflects off a material and exactly reverses into a vector aimed back toward its origin, is that truly time reversal—or merely spatial inversion with phase correction? Reasonable physicists disagree.
Instead of reflecting an electromagnetic wave in space, as with a mirror, this metamaterial reflects it in its evolution, reconstructing the wave’s prior state. This has practical implications for imaging, signal correction, and communications—but not for undoing history.
Unfortunately.
If it were otherwise, transmission-line metamaterials scaled to the size of warships, combined with technology capable of converting warships into electromagnetic waves, would allow defense contractors to build a ship, time-reverse it, and then charge again to build it once more—ad infinitum. One would only need to convert the ship into an electromagnetic wave before reflecting it in the time-reversal medium, and ensure that only the portion striking the material is reversed.
Physics, regrettably, refuses to cooperate.
cf https://www.popularmechanics.com/science/a69717180/time-reflections-are-real-scientists-confirm/
Gemini added- and ChatGPT edited-
A Philosophical Note on Time, Order, and Reversibility
What makes the CUNY “time-reversal” experiment philosophically significant is not that it sends anything into the past, but that it destabilizes a deeply embedded intuition about what time is. In everyday experience, temporal order feels inseparable from causal order: first causes, then effects; first signals, then echoes. Ordinary reflections reinforce this intuition. They reverse direction in space while leaving temporal sequence untouched.
The temporal reflection demonstrated in this experiment breaks that alignment. The wave remains within forward-moving space-time, yet its internal chronology is inverted. The last part of the signal becomes the first to return. This reveals that temporal order, at least at the level of physical signals, is not an absolute structure imposed by the universe, but a contingent feature arising from how systems interact with their environments.
From a philosophical standpoint, this supports a view of time closer to a relational or structural conception than a purely linear one. The experiment shows that what we ordinarily call “the flow of time” may be less fundamental than the ordering rules governing information, energy, and phase. When those rules are altered—here, by a global and instantaneous change in the medium—the apparent arrow of time within a system can be locally reversed without violating causality or thermodynamics at the larger scale.
This distinction is important. The universe’s macroscopic arrow of time—associated with entropy increase—remains intact. What is reversed is not entropy or causation itself, but the ordering of a signal’s internal history. In this sense, the experiment demonstrates that temporal direction is not a single monolithic property of reality, but something that can meaningfully differ across levels of description.
Philosophically, the result resonates with long-standing debates about whether time is something that flows or something that is structured. The temporal mirror suggests that “earlier” and “later” are not always intrinsic properties of events, but can depend on the physical context that mediates them. Time, here, behaves less like a universal river and more like a coordinate system whose orientation can be locally inverted.
In this light, the experiment does not imply that the past is accessible or revisable. Rather, it reveals that chronology itself is a physical variable, not merely a metaphysical given. The significance lies not in undoing time, but in showing that the ordering of events—what comes before and what comes after—can be engineered, at least for waves, without contradiction.
Seen this way, temporal reflection is not a curiosity at the edge of physics, but a concrete example of how time may be better understood as an emergent feature of physical interactions, rather than an absolute backdrop against which those interactions unfold.
ChatGPT-
Temporal Reflection and McTaggart’s Two Orders of Time
The peculiar significance of the CUNY temporal-reflection experiment becomes clearer when viewed through the framework introduced by J. M. E. McTaggart. In his famous analysis, McTaggart distinguished between two ways of ordering events in time: the A-series and the B-series.
The A-series orders events as past, present, and future. It is the time of lived experience, of becoming, anticipation, and memory. The B-series, by contrast, orders events simply as earlier than or later than one another. It contains no moving present and no intrinsic direction—only relational structure.
McTaggart argued that the A-series is internally contradictory and that time, as we ordinarily experience it, is therefore unreal. Whether one accepts that conclusion or not, the distinction itself has proven remarkably durable.
Ordinary reflections preserve both series. When a wave reflects off a mirror, its spatial direction changes, but the temporal order of the signal does not. The first part of the wave remains earlier than the later parts, and the A-series alignment—cause preceding effect—remains intact.
The temporal reflection demonstrated in the CUNY experiment behaves differently. While the wave remains embedded in the forward evolution of space-time, the B-series ordering of the signal’s components is inverted. What was later becomes earlier within the reflected wave. The internal “earlier-than / later-than” relations are flipped, even though no event becomes past-future in the A-series sense.
This is the key philosophical point: the experiment shows that B-series ordering is a manipulable physical property, not a metaphysical absolute. The universe’s A-series—its overall thermodynamic direction and causal stability—remains untouched. But the relational structure that orders events within a system can be reversed under the right physical conditions.
In McTaggart’s terms, the experiment offers empirical support for the idea that what feels like the “flow” of time may not be fundamental at all. The A-series may be a feature of how conscious agents inhabit physical processes, while the deeper structure of time resembles the B-series: a network of relations that can, in certain contexts, be locally re-ordered without contradiction.
Importantly, this does not vindicate McTaggart’s stronger claim that time is unreal. Rather, it refines the debate. The temporal mirror shows that chronology is not identical with causality, and that temporal direction is not globally imposed but locally emergent. What we call “time” may be a layered phenomenon: rigid at the cosmological scale, flexible at the level of information-bearing waves.
Seen through this lens, temporal reflection is not a violation of time but a demonstration of its structure. It suggests that the arrow of time is not a single, indivisible feature of reality, but a composite of thermodynamic, informational, and relational constraints—some of which can, under precise conditions, be reversed.
Temporal Reflection and the Block-Universe View
The CUNY temporal-reflection experiment also invites comparison with the so-called block-universe conception of time, often associated with Minkowski and later with Einstein’s interpretation of relativity. On this view, the universe is not something that unfolds moment by moment, but a four-dimensional structure in which all events—past, present, and future—coexist as fixed relations within space-time. Nothing objectively “flows”; change is a feature of how observers are embedded within the block.
At first glance, temporal reflection fits comfortably within this picture. If time is fundamentally a network of relations rather than a moving present, then reversing the internal order of a wave poses no metaphysical problem. The wave’s history is simply another path through the block, one in which the ordering of informational states runs opposite to our usual expectations. From this perspective, the experiment looks less like a paradox and more like a controlled re-routing of events within an already-given structure.
However, the experiment also exposes a tension in the block-universe view. While the block treats all temporal relations as equally real and fixed, temporal reflection shows that some temporal orderings are dynamically produced, not merely passively “there.” The inversion of a wave’s chronology requires an active, global change in the medium—an intervention that alters which events are earlier and later within the system. This suggests that at least some temporal relations are contingent on physical processes, not simply embedded in a timeless geometric whole.
This is where the contrast with McTaggart becomes illuminating. McTaggart’s skepticism about the reality of time stemmed from contradictions he saw in the A-series, not from denying relational order altogether. The temporal mirror aligns with this skepticism in an unexpected way: it preserves the overall causal and thermodynamic stability of the universe while undermining the intuition that temporal order is fixed and inviolable at every scale.
In other words, the experiment sits uneasily between the two views. It supports the block-universe claim that time does not fundamentally “flow,” yet it resists the idea that all temporal relations are immutable. The block may exist, but its internal structures appear to be locally rewritable.
Philosophically, this points toward a hybrid position. Time may be globally block-like—anchored by relativistic space-time and thermodynamic constraints—while remaining locally plastic where information, waves, and fields are concerned. Temporal direction, on this account, is not a single cosmic property but a layered phenomenon: rigid at the level of entropy and causation, flexible at the level of signal structure.
Seen this way, the significance of temporal reflection is not that it overturns either McTaggart or Einstein, but that it sharpens the question both left unresolved. The experiment suggests that time is neither a pure illusion nor a fully frozen block, but a structured medium whose ordering principles can be selectively inverted without breaking the universe as a whole.
For philosophy, this is a rare and valuable case: a concrete physical result that forces us to distinguish more carefully between time as experienced, time as ordered, and time as physically instantiated—and to recognize that these may not always coincide.
Temporal Reflection and Whitehead’s Process Philosophy
If the block-universe treats time as static structure and McTaggart dissolves it into logical contradiction, Alfred North Whitehead offers a third position: time as process. For Whitehead, reality is not made of enduring substances laid out in space-time, but of events—what he called actual occasions—each coming into being, achieving its moment of definiteness, and then perishing. Becoming, not being, is fundamental.
On this view, time is not something that exists independently of events. It is the cumulative advance of novelty as occasions succeed one another. Crucially, this advance is irreversible. Once an occasion has perished, it becomes part of the settled past, contributing to the conditions of future events but never re-entering the process as something that can be reordered or undone.
From a Whiteheadian perspective, the idea of temporal reflection is immediately suspect—not because it violates physics, but because it appears to violate the metaphysical asymmetry between past and future. If the order of events within a wave can be inverted, does this not amount to reversing becoming itself?
The resolution lies in recognizing what is and is not being reversed. The CUNY experiment does not reverse the succession of actual occasions. The global process of becoming continues uninterrupted. What is inverted is the internal ordering of information within a physical system, not the ontological order of events as such.
In Whitehead’s terms, one could say that the temporal mirror operates at the level of prehensions—the ways in which an occasion takes account of data from the past—rather than at the level of the occasions themselves. The wave’s structure is reorganized so that later informational components are made available earlier within the reflected signal, but no actual occasion is re-created, un-perished, or reinserted into the past.
This distinction preserves Whitehead’s core insight: becoming remains one-way. The experiment does not undo the creative advance; it exploits the fact that not all temporal asymmetries are ontological. Some belong to how information is carried, stored, and transmitted within processes, rather than to the processes themselves.
At the same time, the experiment poses a subtle challenge to process philosophy. Whitehead emphasized that relations to the past are inherited in a fixed order. Temporal reflection shows that, at least for certain physical systems, the order in which past data is re-presented to the present can be actively reshaped. This suggests that while becoming itself may be irreversible, the structure of inheritance is more flexible than process philosophy often assumes.
The philosophical upshot is a refinement rather than a refutation. Whitehead is right that time is fundamentally about becoming, not geometry. But the temporal mirror shows that becoming does not uniquely determine informational order. The arrow of process and the arrow of signal are related, but not identical.
In this light, temporal reflection appears not as a metaphysical anomaly, but as a boundary case—one that reveals a layered conception of time. At the deepest level, there is irreversible creative advance. Above it sits a domain of relational and informational structures whose temporal orientation can, under precise conditions, be inverted.
For readers inclined toward process thought, this may be the most important lesson of all: reversibility at the level of form does not entail reversibility at the level of becoming. Time remains real, creative, and asymmetric—yet the ways it is encoded and manipulated within physical systems are far richer than ordinary experience suggests.
